A local on-site wireless monitoring network consists of remote monitoring devices, a central master device for controlling and collecting information from the remote devices, and distributed repeating devices (repeaters). The repeaters provide the means of expanding the communication coverage of the monitoring system by relaying messages to and from the remote devices and the master. Such a monitoring network is useful in many applications, such as, for example, utility meter monitoring, heating ventilation and air conditioning (HVAC) systems, and security systems.
In a simple form, the repeating network includes broadcast type repeaters that receive messages and rebroadcast the message to any other repeating device so that the message can propagate through the network, ultimately arriving at the master device. In such a system, there are no acknowledgment messages between broadcast rounds, as broadcast implies that it is not known who the intended or appropriate receiver should be. Such broadcast systems require little intelligence and are relatively easy to implement and install in practical application. However, such broadcast systems are inherently inefficient in that messages are re-broadcast redundantly in all directions and are received by other repeaters that are further away, as well as closer, to the master. Generally, the master will receive the same message multiple times from multiple paths through the network. This redundancy, although inefficient, is required to ensure a high probability of successful communication of a message from a remote device to the master through the network. In order to avoid endless loops of repeating the same message between two or more repeaters, some method must be employed to limit the number of times that a message is repeated. Limiting the number of times a message is repeated must be balanced with maximizing redundancy to achieve a suitably high probability that the message will ultimately make it to the master. However, limiting the number of times a message is repeated also limits the number of layers of repeaters that can be employed, thus limiting the range of the system.
An alternative to a broadcast network is a directed network where communication between repeaters is more efficient, in that the same message is not repeated unnecessarily, and also more effective at completing communications successfully. A directed network requires a known path from one repeater to the next as a message moves through the network. This known path allows the network to be more efficient and effective in delivering messages from a remote device to the master. Every message passed from one repeater to the next is not repeated by all other repeaters that may have received the message, as happens in a broadcast type system. Every received message is confirmed by an acknowledgment back to the sender so that arbitrary redundancy is not required. Much less communication traffic is generated in a directed network for any given message. Since every passed message is confirmed, a redundant attempt is required only if no acknowledgment occurred. If an attempted communication is not confirmed, an alternate path can be attempted. Thus, the capabilities of a directed network require much more intelligence in the system. For example, every repeater within the system must know where it is within the network, and in relation with other repeaters with which it can communicate in order to propagate a message toward the intended receiver.
In a directed network, layering of repeaters is necessary in order to propagate a message in the intended direction. Each repeater must be assigned an appropriate layer designation. In order to accommodate a relatively large scale system, it may be necessary to repeat an originated message several times, through several layers of repeaters, to get the message to the master. Thus, in such a system, a repeater receives a message, and propagates it to either another repeater which is closer to the master, or to the master itself. Thus, each repeater must be assigned to retransmit messages to another repeater. This assignment of repeaters to layers, and to communicate with specified other repeaters, can become complex.
Referring to FIG. 1, a diagram illustrating a free space wireless communication network 100 is now discussed. In the communication network 100, there is a master device 104, which communicates with a plurality of remote devices 108. As mentioned above, in order to expand the range of such a communication network 100, layers of relay devices may be used. In the free space example illustrated in FIG. 1, three layers of relay devices are illustrated, a first layer having first layer repeaters 112, a second layer having second layer repeaters 116, and a third layer having third layer repeaters 120. The communication network 100 can be used in a number of applications, such as, for example, utility metering where the remote devices 108 transmit usage information to the master device 104 for a particular utility meter. In such a system, the remote devices 108 are connected to a utility meter, such as a electricity or gas meter, and periodically transmit usage information for the utility meter to the master device 104. Information collected at the master device 104 may then be used for a variety of purposes, such as billing or demand forecasting. The communication network 100 may also be used in other applications, such as in a heating, ventilation, and air conditioning (HVAC) system, where the master device 104 may monitor temperature of other environmental conditions present at the remote devices 108, and adjust environmental conditions based on the information received from the remote devices 108. Furthermore, the communication system 100 may be used in applications where the remote devices 108 are mobile, such as a delivery service or a repair/maintenance service where a master device 100 may monitor the status of deliveries being made by a particular courier or the status of a particular repair/maintenance person through periodic check-ins by the courier or repair/maintenance person having a remote device 108 in their possession.
Referring now to FIG. 2, a practical network 101 is illustrated. As will be understood, the conceptual free space communications network 100 of FIG. 1 is generally not possible to implement. This is due to interference in the signals between a repeater and another repeater or a master or remote. Interference can be the result of, for example, localized radio interference, obstacles, topography or dense foliage in the transmission path. Accordingly, although a repeater may physically be closer to a master than another repeater, the closer repeater may not be able to wirelessly communicate with the master. Hence, the closer repeater will communicate with another repeater, which may be further away, in order to communicate with the master. As illustrated in FIG. 2, a master 104 communicates with a plurality of remote devices 108 through a number of layers of repeaters. As illustrated, a first level of repeaters 112 can communicate directly with the master 104. A second level of repeaters 116 communicates with the first level of repeaters 112, and a third level of repeaters 120. In the illustration of FIG. 2, the network has a fourth level of repeaters, 124, a fifth level of repeaters 128, a sixth level of repeaters 132, and a seventh level of repeaters 136. As can be noted from FIG. 2, a number of repeaters may be required to connect a remote 108 to the master 104 when obstacles are present. Furthermore, in such a practical network, it is common for new obstacles to enter the network, and for existing obstacles to disappear. Such situations may arise, for example, when buildings are erected in a communication path, buildings or trees are removed, or a source of radio interference is introduced or taken away. In such a changing network environment, it becomes increasingly difficult to maintain the directed network configuration, as repeaters have to change the repeater with which they communicate, and often require a change in their layer number. Accordingly, it would be advantageous to have a system in which repeaters may transmit status or maintenance messages for the purpose of keeping a current, and efficient, directed network.